Ferriresonant memory system



Aug. 12, 1969 I. a. AKMENKALNS 3,

' FERRIKESONANT MEMORY SYSTEM Filed Oct. 22. 1965 MICROWAVE 1 OSCILLATOR f BIPOLAR I I A N. SIGN L CE I 2 F Q m V J a Y FIG. 1 SA A IINVENTORS IVARS c. AKMENKALNS ROGER L. GAMBLIN PHILLIP A. LORD FIG. 4

A TTORNE Y United States Patent 3,461,441 FERRIRESONANT MEMORY SYSTEM Ivars G. Akmenkalns, 'Endicott, and Rodger L. Gamblin and Philip A. Lord, Vestal, N.Y., assignors to International Business Machines Corporation, Armonk, N.Y.,

a corporation of New York Filed Oct. 22, 1965, Ser. No. 500,941 Int. Cl. Gllb 5/62 US. Cl. 340-174 6 Claims ABSTRACT OF THE DISCLOSURE A microwave absorption and non-destructive memory system in which a ferrite element operating at its gyromagnetic resonant frequency presents a high or a low loss depending on the magnetic state of the ferrite element. In a first stable state, the ferrite element absorbs microwave energy and therefore presents a high loss. In a second stable state, the ferrite element absorbs less microwave energy and therefore presents a low loss. The ferrite elements are interrogated by means of a helical waveguide structure which is energized at one end by means of a microwave source and has the other end connected to a sense amplifier for determining the amplitude of the microwave energy transmitted through the ferrite element. The helical waveguide is wound over the outside of the ferrite element.

This invention relates in general to magnetic memory storage systems and, more particularly to an improved non-destructive read-out (NDRO) memory system.

A novel NDRO memory element operating upon the principle of gyromagnetic resonant absorption is disclosed by R.L. Gamblin et al. in their co-pending application Ser. No. 502,008, and assigned to the assignee of the present invention. The present invention is directed to an improved embodiment of an NDRO memory element.

It is an object of the instant invention to provide an improved embodiment of a NDRO memory element operating upon the principle of gyromagnetic resonant absorption.

It is another object of the instant invention to provide a NDRO memory element having an improved gyromagnetic resonant absorption characteristic caused by a helix being positioned around a cylindrically shaped ferrite storage medium.

It is a still further object of the instant invention to provide an improved embodiment of a NDRO absorption memory element employing a ferrite element and a helical read-out coil having a preselected pitch and/ or pitch angle.

It is a further object of the instant invention to provide an improved embodiment of a NDRO absorption memory element employing a circularly polarized ferrite element and a helical read-out coil including impedance matching circuits integral with the coil.

It is another object of the instant invention to provide an improved NDRO absorption memory element suitable for high production rates by having a helical read-out coil suitably positioned around its associated ferrite element so as to be adapted to electrodepositing manufacturing techniques yet give improved isolation characteristics.

It is an additional object of the present invention to provide an improved NDRO absorption memory element employing a helical coil wrapped around a ferrite core wherein the electrical length of the helix wrapped around the core is one or more integral number of the wave lengths of the associated microwave signal.

According to these and other objects, the present invention provides an improved microwave NDRO memory element operating on the principle of gyromagnetic resonant absorption and having improved operating characteristics. Briefly, the present invention contemplates the use of a ferrite toroid as a magnetic storage element, a Gunn Effect or tunnel diode oscillator as a source of microwave signals, a uniquely wound helical coil wrapped around the toroid and connected to the microwave source as a means of circularly polarizing the signals generated in the source, and a sense amplifier connected to the remaining end of the helical coil to determine the level of microwave energy passing through the coil. More specifically, selectable half-select write lines thread each magnetic storage element for driving it into either of its two stable states of remnant magnetization wherein a condition of gyromagnetic resonant absorption is generated. The passage of a highly circularly polarized micro wave signal, oscillating substantially at the gyromagnetic resonant absorption frequency of the ferrite, over the associated helical coil samples the state of the core in the following way. When the magnetic field around the helix is rotating in the same sense as the electrons are precessing in the toroid, absorption occurs and the microwave signal is substantially absorbed indicating one remnant state of magnetization of the toroid. When the magnetic field of the helix is not rotating in the same sense as the electrons in the magnetized toroid, substantially no absorption occurs indicating the other remnant state of magnetization of the toroid. Since there is only one helix wound on the core in the above description, the only unknown quantity is the remnant state of the toroid. Similar systems can be built using oppositely wound helices while maintaining only one remnant state of magnetization.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying figures; wherein FIG. 1 is a schematic view of an embodiment of the instant invention suitable for use as a memory element;

FIG. 2 is a schematic view of an embodiment of the instant invention suitable for use as a logic element;

FIG. 3 shows the instant invention employing a plated helical coil; and

FIG. 4 is a graph showing the improved characteristics obtainable by this improved NDRO absorption element.

The same numerals are used to identify the same elements shown in the different views.

Referring to FIG. 1 there can be seen a microwave absorption (MA) element 1 employing a helical coil 2 wrapped on an outer wall 3 of a ferrite toroid 4. The term toroid refers to that class of geometric shapes having an inner wall 5 forming an interior bore 5a and providing an air gap suflicient to prevent non-azimuthal magnetization and to assure circular polarization when subjected to a magnetizing current pulse on a line 6. The term ferrite is used in this description to identify that class of magnetic metals which possess extremely high resistivity and tensor permeability and, which exhibit the resonant absorption phenomenon when operating with a properly polarized microwave signal.

More specifically, the proper conditions for exhibiting the resonant absorption phenomenon include the switching of the ferrite toroid 4 into its state of magnetization so that one electron in the ferrite finds itself in the field of all the other electrons. The one electron is not free to move alone in response to an external magnetic field because of exchange interactions but rather, must respond to the external magnetic field together with its neighboring electrons. Because an electron has both a magnetic moment and angular momentum, it acts like a small magnetized top when exposed to an external magnetic field.

When the electron is in this external magnetic field, the field attempts to rotate the electron so that the two become aligned. Like all tops upon which such forces act, however, the electron does not line up with the field but instead, precesses or swings about the field direction. With a magnetic field which is rotating in the same sense as the electron precesses, the electron absorbs energy from the field and tends to become disaligned therefrom. This process of the precessing electron tending to absorb energy from an external magnetic field is generally known as gyromagnetic resonant absorption. When the external magnetic field is rotating in a sense opposite to that in which the coupled electrons are precessing or the field is oscillating at a substantially different rate of rotation, the magnetic field passes through the ferrite substantially undiminished in intensity.

In the case of isolated electrons, the magnetization state can be disaligned from a steady field by means of the circularly polarized field. In a ferrite however the individual electrons are coupled together preventing actual disalignment from the steady magnetic field in which the electron is placed, but rather the rotating magnetic field is absorbed by the ferrite and converted to heat.

Referring to FIG. 4, the placement of the helix 2 on the outer wall 3 of the toroid 4 increases the discrimination between the two remnant states of magnetization of the toroid in as short an axial length of ferrite as possible. The curve B represents the discrimination for an element having its coil on the outside and the curve A represents the discrimination for an element having its coil on the inside. The vertical numbers are in decibels and the horizontal numbers refer to gigacycles per second. An analysis of the magnetic field around a core indicates that the discrimination ratio between one direction of circular polarization to the other direction of circular polarization is highly dependent upon certain characteristics of the helix and the location of the ferrite material with reference to the helix. More specifically, for a tightly wound helix there is little magnetic field on the outside of the helix as compared to the magnetic field on the inside of the helix. Additionally, for a tightly wound helix, the circular polarization on the inside of the helix lies in a perpendicular plane containing the axis of the helix.

The condition that gives the maximum circular polarization ratio on the inside of the helix is that the electrical length of a signal traveling along the helix is shorter than the circumference of the helix. There are restrictions as to how tightly wound the helix 2 can be. One reason is that a spacing 7 cannot be tight as compared to the size of the wire used in winding the helix since the wire in each coil must remain physically distinct. It has been found that when extremely small diameter wire is used and a pitch angle 8 is made very small, the impedance of the helix reaches such a high level that microwaves no longer can be transmitted through the helix.

It has been found experimentally that a pitch angle 8 of approximately 01:0.025 radian gives superior results. Additionally, it has been found that making an electrical length 10 of the helix 2 one or more integral values of wave length of the microwave signal gives the best operating characteristics. The use of one or more integral values of wave length provides a means of matching the high impedance of the helix with the remaining circuitry.

In operation, a bi-polar pulse generator 12 and its associated drive winding 6 operates to switch the core 4 into either of its states of remnant magnetization by opposite polarity pulses. A Gunn Effect or tunnel diode microwave oscillator furnishes a microwave signal to one end of the helix 2 by a first strip line 14. A complete description of a Gunn Effect oscillator is found in US. Patent 3,365,583 assigned to the assignee of the present invention. A sense amplifier 16 is connected to the other end of the helix 2 by a second strip line 18 to determine the energy value of the microwave signal passing through the helix, The coil 2 generates a highly circularly polarized wave having a magnetic field rotating in one direction. When the remnant state of the core 4 is in one of its stable states, a resonant absorption phenomenon occurs between the microwave signal and the core and substantially no portion of the microwave signal reaches the sense amplifier. However, when the remnant state of the core 4 is in its other stable state, no resonant absorption phenomenon occurs and the microwave signal passes substantially undiminished to the sense amplifier 16.

Referring to FIG. 2, a second embodiment of the instant invention is shown suitable for use in computer logic circuits. For its use in computer logic circuits, maximum energy transmssion through the helix is required for that remnant state of magnetization of the core 4 for which resonant absorption does not occur. Therefore, it has been found desirable to add an integral input impedance matching section 20 to one end of a resonant absorption section 22, and to add an integral output impedance matching section 24 to the other end of the section 22. The section 22 is made on integral number of wave lengths long. Section 22 is made an integral number of wave lengths long for the same reasons brought out in the discussion concerning the section 10 shown in FIG. 1. The sections 20 and 24 to provide impedance matching with the remaining circuitry so that a maximum amount of power is transmitted through any one logic element.

In addition to the restrictions previously desirable the following relationship must be maintained for the radius of the helix:

where a=radius of the helix )v=th6 wavelength of the helix x=x tan a 0=pitch angle of the helix in radians 7\,,=C/ V C=speed of light in air, and V=operating frequency With the foregoing equation, the physical dimension of the helix and core are related to the frequency of the signal passing down the helix and the spacing coils.

FIG. 3 shows an additional embodiment of the instant invention. A cylindrically shaped support member 30 of non-magnetic material is formed with a central bore 31 and a plurality of notches 32 into which a ferrite material is placed in the form of a plurality of cores 34. A helical coil 36 is formed by depositing a layer of copper over an entire outside surface 38. The surface 38 comprises in part the cores 34 and the support member 30. The excess copper is etched away leaving a helical coil 36.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

. 1. A non-destructive readout memory system comprismg,

a cylindrically shaped ferrite toroid being formed with an axial bore and an outer wall,

said toroid having a gyromagnetic resonant absorption frequency,

first means for selectively magnetizing said toroid to a first stable state of remnant magnetization or to a second stable state of remnant magnetization,

said magnetized toroid having substantially all electrons with a first sense of rotation in a first stable state of remnant magnetization and having substantially all electrons with a second sense of rotation in a said second stable state of remnant magnetiza, tion,

a source of microwave signals operating at substam tially said resonant absorption frequency,

a helical coil wound around said toroid and connected to said source for circularly polarizing said microwave signals in said first sense of rotation,

said toroid in said first state absorbing said microwave signals and said toroid in said second state passing said microwave signals substantially undiminished therethrough, and

sense amplifier means connected to said coil for determining the absorption of said microwave signals and the passing of said microwave signals.

2. A non-destructive readout memory system as recited in claim 1, wherein said coil comprises a plurality of turns having a constant pitch angle.

3. A non-destructive readout memory system as recited in claim 1, wherein said coil is in contact with said outer wall.

4. A non-destructive readout memory system as recited in claim 1, wherein said coil is formed with an electrical length equal to an integral number of wavelengths of said frequency, and the pitch angle of said helical coil is substantially constant.

5. A microwave absorption system comprising,

a cylindrically shaped ferrite toroid being formed with an axial bore and an outer wall,

a helical coil formed with a plurality of turns having a constant pitch angle and arranged into an input impedance matching section and an absorption section and an output impedance matching section,

a microwave oscillator connected to said input impedance section for generating a signal having a substantially constant wavelength,

each of said sections being an integral number of said wavelengths in length,

said absorption section being positioned in contact with said outer wall, and

output means connected to said output impedance matching section for sensing said microwave signal transmitted over said coil.

6. A non-destructive readout memory system comprisa cylindrically shaped magnetized ferrite toroid being formed with an inner bore and an outer wall,

said toroid having a gyromagnetic resonant absorption frequency,

said magnetized toroid having substantially all electrons with a first sense of rotation in a first stable state of remnant magnetization and having substantially all electrons with a second sense of rotation in a second stable state of remnant magnetization,

a source of microwave signals operating at substantially said frequency,

a helical coil wound around said toroid and connected to said source for circularly polarizing said microwave signals in said first sense of rotation,

said toroid in said first state absorbing said microwave signals and said toroid in said second state passing said microwave signals substantially undiminished therethrough, and

sense amplifier means connected to said coil for determining the absorption of said microwave signals and the passing of said microwave signals.

References Cited UNITED STATES PATENTS 2,911,554 11/1959 Kompfner et a1. 333-24 XR 2,994,842 8/1961 Treuhaft 3331.1 3,155,941 11/1964 Mims 340-173 OTHER REFERENCES Kriz, T. A., Microwave Readout of Ferrite Memory Storage. IEEE Transaction on Electronic Computers, February 1965, pp. 75-76.

BERNARD KONICK, Primary Examiner G. M. HOFFMAN, Assistant Examiner US. Cl. X.R. 

